Conventionally, foamed resin containers have widely been used as vessels for instant food, juice or the like. Such a foamed resin container is generally produced through a foam molding method in which pre-foamed beads obtained by preliminarily foaming foamable resin beads containing a polystyrene resin and a volatile blowing agent such as butane, pentane or chrolofluorocarbon are loaded in a mold cavity and heated by a heating medium such as steam for foaming the foamed resin containers.
Some of the foamed resin containers are provided with a label which bears information such as a trade name and a maker's name and/or a design such as a vignette printed thereon, or serves to impart an excellent gas barrier property to the foamed resin containers.
Known as a method for providing such information or the like on the surface of a foamed resin container (foamed bead cup), there are a method wherein information or the like is directly printed on the surface of a foamed resin container, a method wherein a label bearing information or the like preliminarily printed thereon is bonded onto a foamed resin container, and a so-called shrink-labeling method wherein a heat-shrinkable film bearing information or the like preliminarily printed thereon is wrapped around a foamed resin container and shrunken by heat.
In the method of directly printing on the surface of a foamed resin container, it is difficult to obtain a sharp printing like gravure or to perform a multi-color printing. In the method of bonding onto a foamed resin container a label bearing information preliminarily printed thereon, a container molding step, a label stamping step, and a label bonding step are separately performed. Therefore, it is required that the label be positioned in place in the label bonding step, so that the process is complicated. In the shrink labeling method using a heat-shrinkable film, the heat-shrinkable film softly adheres on the container so that the film is liable to slip out of the container if the container has an inclined circumferential surface.
To solve these problems, Japanese Unexamined Patent Publication No. 4-331132 (1992) discloses a method for in-mold labeling of a foamed resin container, which includes steps of rolling into a predetermined tubular shape a print paper sheet having a print layer on the outer surface and a heat-seal layer on the inner surface of a paper base, setting the print sheet in a cavity mold, fixing the print sheet on the inner wall of the cavity mold by evacuating the cavity through a multiplicity of gas vent holes provided in the cavity mold, matching the cavity mold with a core mold, loading foamable resin beads into a gap defined between the print paper sheet and the core mold for foam molding, and fuse-bonding the print paper sheet onto the resulting foamed resin container by applying heat thereto for the foamed resin molding.
However, the aforesaid method involves complicated process steps because the print paper sheet is once punched out into a predetermined configuration and then the punched sheet should be rolled into a tubular shape. Further, the print paper sheet which has the print layer and the heat-seal layer provided, respectively on the opposite surfaces of the paper base is inferior in the moisture resistance and gas-barrier property. Therefore, the paper sheet absorbs steam applied when the foamed resin container is molded, so that the printing is liable to be blurred. In addition, because the print layer on the outer surface of the paper base is brought in directly contact with the cavity mold, the printing ink is liable to be transferred onto the cavity mold from the print paper sheet by heat. If the printing ink transfer occurs, the print density on the foamed resin container is reduced, resulting in a printing failure. The ink transferred onto the cavity mold is further transferred onto the next mold product, resulting in successive printing failures.
Since the print paper sheet should be rolled into a tubular shape before the molding, the process steps are complicated, resulting in an increased cost.
To solve these problems of the prior art, it is an object of the present invention to provide a novel process and apparatus for producing a labeled foamed resin container with which employ a thin and less stiff or floppy synthetic resin sheet instead of the paper base and a label obtained by preliminarily printing fine letters and a sharp design such as including smooth gradation on the resin sheet, and is adapted to apply the floppy sheet label in a predetermined position on the foamed resin container by integral molding without rolling the label into a tubular shape before molding the foamed resin container.
It is a more specific object of the present invention to provide a process and apparatus for producing a foamed resin container with a label, in which a sheet which bears printed labels in predetermined portions thereof is continuously supplied and a process sequence from the step of punching a label from the sheet to the step of molding the foamed resin container with a label is readily and continuously performed.